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Friday, February 15, 2019

This is a "Save the Date" notice for an upcoming 1D-2D HEC-RAS 3-day training course I'll be giving in Atlanta on May 7-9, 2019. We'll be covering everything from setting up a 2D model, a 1D-2D combined model, RAS Mapper pre- and post-processing, viewing output, river restoration, to dam/levee breaching. The class will consist of a mix of informative lectures focusing on practical aspects of 1D-2D HEC-RAS modeling and interactive exercises.

Come join me for a great opportunity to learn the tricks of 1D-2D modeling in HEC-RAS and to network with fellow HEC-RAS Users.

If you are interested, please follow the following link and express your interest. We will send more details, including the venue and registration instructions as soon as they are available.

Monday, January 21, 2019

Using RAS Mapper as a GIS tool Part 2:Shifting Web Imagery with World Files

Have you ever tried pulling web imagery into RAS Mapper only to find that it doesn't line up with your existing shape files, terrain surfaces, or other geospatial data? In this second of a three-part series on using RAS Mapper as a GIS tool we'll cover the modification of world files for georeferencing.

In some cases, the misalignment of web imagery may result from an incorrectly applied projection file. If needed, projection files can be downloaded for free from spatialreference.org and other online data sources. You can check the projection of your terrain file by double-clicking on it in RAS Mapper, then select the "Source Files" tab and view the metadata using the Info column.

If you have confirmed that the correct projection file is being used and you are still having issues, there are a few additional workarounds you may wish to try. One option is to select the "Alternate HEC-RAS Raster Warping Method" under "Tools | Options" in RAS Mapper. This method applies the gDAL OGR vector reprojection. I have found this method useful for resolving discrepancies in European data sets in particular.

In some cases, the alternate method doesn't do the trick either. RAS Mapper uses the ESRI projection file format, which as I understand it does not recognize TOWGS84 parameters and in some cases improperly applies the proj.4 projection parameters. In any case, you may find yourself stuck with misaligned web imagery.

One workaround is to save static images of your web imagery and then shift the image to the correct location by making adjustments to the world file (Wikipedia has a good summary of the six lines of code comprising a world file here).

The "World File Calculator" spreadsheet referenced in the video can be downloaded here:

Here are the steps covered in the video:

1. Adjust transparency as needed so that you can see a known point in both the web imagery and in the survey or LiDAR data.
2. Using the measure tool in RAS Mapper, click on a known point from the web imagery (with incorrect location), then double-click on the the same known point based on the correct location.
3. Select "Copy coordinates to clipboard".
4. Zoom to preferred extents for results and save view (click here for further details on saved views and static imagery).

5. Right-click on web imagery and select "export layer". Note: RAS Mapper currently has two export options: tif and jpg. The tif format will embed the metadata and georeferencing information into the encoded text of a geotif file without generating a separate world file. A tfw file can still be created to override the embedded georeferencing, but I suggest using the jpg format so that the world file is automatically generated. Save the image (I suggest creating an "aerial imagery" subfolder within the current project's directory structure to store static images).

6. Open the world file calculator spreadsheet.

7. Paste the coordinates from RAS Mapper into the blue cell.

8. Open the newly created jgw file (jpg format world file) in a text editor and copy the values.

9. Paste the values into the "Original World File" column of the spreadsheet.

10. Copy the "New World File" values over the original values in the jgw file, save, and close.

11. Under Map Layers in RAS Mapper, right-click and select "Add Existing Layer". Be sure to drag down file types to show all image files and browse to the newly created file.
12. Adjust transparency as needed to confirm common points are now co-located.

The process can be repeated to fine-tune the positioning. Because a static image won't be pyramided like web imagery, you will unfortunately need to complete these steps at every desired zoom level and view extent, the but the process of saving static images allows you to control the appearance of your figures without having to worry about losing your internet connection while presenting or viewing results.

Note that these steps assume the units and north alignment are the same (or close enough) between the data sets and that the static image can be simply shifted without scaling or rotation factors, which we'll cover in more detail in our next post.
Please let us know any feedback or suggestions for improvements or additional efficiencies in adjusting web imagery.

Please
look closely at this document, as there as a few issues that are potential
computational problems.Specifically
issues 1, 2, 5, and 7.Please review
these issues closely.If you have any of
these situations use the suggested work around, or solution to get past the
issue.Everyone should look at issue 1
and 2, as they are possible in many models.

Sorry
for any inconvenience this may cause you.Keep letting us know if you find other problems with the software.

Friday, January 11, 2019

One of the most anticipated new features soon to come in the next major version of HEC-RAS (Version 5.1) is the option of running unsteady 1D reaches with a finite volume solution scheme. This will be a fantastic addition to HEC-RAS. Gary Brunner recently gave me a brief overview of the new finite volume feature we can expect. But before you ask, there is no set release date for Version 5.1 yet. But I'm hoping we'll see it within the next year or two.

1D Finite Volume Solution Algorithm

By Gary W. Brunner, P.E., D.WRE

Senior Technical Hydraulic Engineer

Hydrologic Engineering Center

A brand new solution algorithm has been developed for 1D
modeling.A Finite-Volume solution
approach, similar to what was added for 2D modeling will be available for 1D
modeling in HEC-RAS version 5.1.

The current 1D Finite Difference solution scheme has the
following deficiencies:

Cannot handle starting or going dry in a cross section

Low flow model stability issues with irregular cross section data

Extremely rapidly rising hydrographs can be difficult to get stable

Mixed flow regime (i.e. flow transitions) approach is approximate

Stream junctions do not transfer momentum

The new 1D Finite Volume approach has the following
positive attributes:

Can start with cross sections completely dry, or they can go dry during a simulation (wetting/drying)

Junction analysis is performed as a single 2D cell when connecting 1D reaches (continuity and momentum is conserved through the junction).

Additionally, the new 1D Finite Volume approached is
solved in the same matrix as the 2D equations.Solving in the same matrix allows for faster 1D/2D model solutions and
more accurate flow transfers between 1D and 2D elements.The equations are solved together and all
hydraulic connections are updated together on an iteration by iteration
approach, rather than separately, as in previous versions of HEC-RAS.

Monday, January 7, 2019

Using RAS Mapper as a GIS Tool Part 1:Removing Bridge Decks from Terrain Surfaces

This is the first in a three-part series on using RAS Mapper as a GIS tool. In this post we'll cover the removal of bridge decks from terrain data.

This topic comes up fairly frequently, since LiDAR data may be inconsistent in terms of the inclusion or exclusion of bridge decks. Depending on how you would like to model a bridge, you may prefer to have the bridge deck represented as terrain or as a deck/roadway defined with station/elevation points (in which case the deck geometry might be best excluded from the terrain data). In either case, you may find yourself needing to modify terrain data to suit your modeling needs.

In a previous post on terrain modification, we covered how to burn channels, levees, buildings, basins, and other features into your terrain surface using RAS Mapper. One application we left off (because it is the example covered in the HEC-RAS manual) is the removal of bridge decks; given some of the feedback we received on the previous post, we thought it might be worth including bridge decks in the process as well.

The process of removing a bridge is actually quite simple, as is the process of inserting some basic deck geometry into your terrain data. We walk through the complete steps for both removing and adding a bridge in less than 5 minutes in this video walk-through:

Here's a screen shot of Page 2-11 in the HEC-RAS 2D User Manual showing a bridge deck included in the terrain data and then removed from the terrain data. Now you see it, now you don't:

The following images are courtesy of Cameron Paintin from Riley Consultants, who applied these steps for a project in New Zealand.

Here is the terrain surface with the bridge deck in it:

Here is a satellite image with the bridge:

In this screen shot, Cameron has drawn a river reach with cross sections on either side of the bridge:

This process can be repeated with additional reaches for any other bridges in your terrain. The following screen shot shows the interpolation surface created by the bounding cross sections:

And the final image shows interpolation surface on top of the terrain to blend out the bridge:

Let us know what you think or if you have other suggestions for improving these processes.

Advances in HEC-RAS now
allow for improved simulation of overbanks using 2D Flow Areas. Coupled 1D/2D
models where 1D cross-sections represent the bank-to-bank cross-section data
and 2D flow areas represent overbank areas has greatly improved the accuracy
and robustness of HEC-RAS models. This is particularly the case in flat, urban
areas with significant overbank flow paths.

These coupled 1D/2D models
have highlighted several simplifications and shortcomings of the traditional HEC-RAS
Junction methodology. Note that the standard method is still required in 1D
steady flow modeling. The following
points suggest an alternative Junction method is worth considering when
building a coupled 1D/2D model.

1D to 2D offline flow transfer over the junction length is
not possible in HEC-RAS. In other words,
a lateral structure cannot span across a junction. In complex confluences, this
transfer region may be critical. Simply reducing the distance between bounding
cross-sections to minimize this region may not be an option depending on the
channel and bank alignments (see Figure 1).

The volume of water within the bounding cross-sections of
junctions is not accounted for, whether forcing the water surface elevation to
match the downstream bounding cross-section or using the Standard Step one
dimensional Energy equation. Both solution techniques simplify the hydraulics
of the region, and in particular, the main reach which conveys the greatest
volume (see Figure 1).

Simplification
of Junction hydraulics has been “accepted” as reasonable, as demonstrated by
the following guidance from the USACE-HEC:

Friday, December 7, 2018

Webinar: Dam Breach Modelling

Colleagues-

I'm honored to join Krey Price and Bill Syme in presenting a brief webinar on dam breach modeling hosted by ICEWaRM and the Australian Water School. Half hour presentation followed by discussion and a Q&A session. Please join if you can.

The different approaches to generating the breach hydrograph, the numerical modelling of downstream flood inundation, benchmarking of solution schemes, and uncertainties associated with the modelling will be presented and explored.

WELCOME TO THE RAS SOLUTION

You've arrived at The RAS Solution. The best help site for all things HEC-RAS. Use the Search bar to find topics you are interested in. Do you have an idea for a blog post to The RAS Solution? I welcome and encourage guest authors. Please follow the instructions here. I do receive a lot of questions in the post comments. I try to respond to all questions, but sometimes it gets a little busy. Please be understanding. New to HEC-RAS? Here's a video from Practical Engineering on some of the great things that HEC-RAS can do and this post provides some great ideas for getting started with HEC-RAS.

The Author

Chris Goodell, Principal Consultant for H&H at Kleinschmidt Associates, is a former HEC-RAS Development Team member and teaches HEC-RAS courses around the world. He is the author of the popular book "Breaking the HEC-RAS Code."

Hey RAS Users- This is a "Save the Date" notice for an upcoming 1D-2D HEC-RAS 3-day training course I'll be giving in Atl...

Background imagery: Columbia River Delta. Courtesy of Google Earth.

"Breaking the HEC-RAS Code"

This book covers one of the most powerful, yet relatively unknown features available in HEC-RAS: the HECRASController! The HECRASController API has a wealth of procedures which allow a programmer to manipulate HEC-RAS externally by setting input data, retrieving input or output data, and performing common functions such as opening and closing HEC-RAS, changing plans, running HEC-RAS, and plotting output.

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